1. Field of the Invention
The invention relates in general to wireless communication, and in particular, to timing synchronization in wireless communication systems.
2. Description of the Related Art
Wireless communication systems provide voice, video, data, and signaling communication services that are widely used. For example, European Telecommunication Standard Institute (ETSI) has specified a Global Standard for Mobile Communication (GSM) that uses time division multiple access (TDMA) over radio frequency (RF) channels.
The wireless communication systems cover a geographical area that is subdivided into communication cells served by at least one base station, which together provide communication coverage to a service area. The base station communicates with mobile stations over downlink and uplink RF channels to provide the wireless communication service. The RF channels are subdivided into a number of time slots or logical channels during which data bits having various burst formats are communicated. GSM specification defines these formats as: normal burst (NB), access burst (AB), frequency correction bursts (FB), synchronization burst (SB), and dummy burst. Voice, video, and text data are communicated by the NB data bursts in designated as traffic channels (TCH). Signaling data pertaining to call management within the system are communicated over control channels using one of the NB, SB or FB burst. The remaining data bursts incorporate training sequences that are used by an equalizer to adjust the transmitted data bits at the mobile station.
The mobile station may be a cellular phone, a notebook computer, or a personal digital assistant (PDA) that employs portable power storage cells such as batteries, with inherently limited storage capacity, require effective power management solution. In one example of the power management solution, the mobile station uses a low clock speed when inactive, referred to as power saving mode, and a high clock speed during normal mobile station operation, known as normal operation mode. The employment of the low clock speed effectively reduce power usage for the mobile apparatus, however, there is a timing error generated every time when exiting the power saving mode as the mobile station switches from a low clock speed to a high clock speed. The mobile station exits the power saving mode when receiving paging information, detecting signal strength or synchronization burst broadcast from neighboring cells, or running applications such as screen saver, Bluetooth, and WIFI connections. When the mobile station executes an application, for example, screen saver, frequently switching between two clock speeds may cause the accumulated timing error to exceed the timing offset tolerance before receiving a next paging data block and performing timing synchronization. The computing processor, such as a digital signal processor (DSP), is unable to performing pattern matching to detect the training sequence if the accumulated timing error exceeds the timing offset tolerance. A solution to this timing error problem is to disable the power saving mode when any of the applications that causes switching between two clock speeds is activated.